Processes of Evolution Genetics Evolution Does natural selection

Processes of Evolution

Genetics + Evolution Does natural selection act directly on phenotype or genotype? http: //1. bp. blogspot. com/_h. W 5 Dg. GNOt. Tw/R 6_w. CJb. HFI/AAAAAB 8/6 Gbcn_y 4 --0/s 320/phenotype. jpg

Genetics + Evolution So what about genes? Higher fitness = more copies of THOSE genes passed on Meet Old Mac. Donald’s pigs. Black pigs are more susceptible to “piggy plague”. What do you think will happen to the number of black alleles in Mr. Mac. Donald’s herd of pigs?

Genetics + Evolution Gene pool – all of the genes present in a population Allele frequency – # of a particular allele in a gene pool compared to the total # of alleles in that pool for the same gene (%) Evolution happens when allele frequency http: //www. brooklyn. cuny. edu/bc/ahp/LAD/C 21/graphics/C 21_Gene. Pool_2. GI

Genetics + Evolution How many B’s are in gene pool? � How many b’s? � 9 15 Allele frequency = 37. 5% B; 62. 5% b bb bb Bb BB Bb bb bb BB

Genetics + Evolution What’s going to happen? Why? 75% B; 25% b Allele frequency changed! bb bb Bb BB Bb bb bb BB 37. 5% B; 62. 5% Trees Darken BB Bb bb BB BB BB Bb BB bb BB BB BB

Genetics + Evolution Natural selection acts on INDIVIDUALS POPULATION evolves Microevolution – small-scale evolution Trees Darken

Variations Need variation for natural selection to work Where does variation come from? � Mutations Ultimate source of new variations Must be heritable Video � Sexual reproduction – shuffles existing genes http: //lovvy. files. wordpress. com/2009/04/mutation. j pg

Microevolution 1. Natural selection is not the only cause of microevolution Microevolution can happen randomly Genetic Drift – random change in allele frequency most common in small populations

Genetic Drift Causes: � Bottleneck effect – disaster indiscriminately kills majority of population – remaining population grows � Founder effect – a few individuals colonize a new habitat

Microevolution 2. Gene Flow – allele frequencies change when individuals move into or out of populations � Tends to reduce differences between populations Only natural selection leads to a better fit between organisms and their environment

Selective Pressures Limited Resources � Leads to competition Interactions Between Species � Leads to coevolution � Predator vs. Prey � Symbiotic relationships Sexual Selection � Leads to sexual dimorphism

How Selection Influences Populations Directional Selection � Favors one extreme � Selects against average and opposite extreme Stabilizing Selection � Favors average � Selects against both extremes Disruptive Selection � Favors both extremes � Selects against average

Evolution Is Not Perfect! Selection only acts on existing variations – it does not cause genetic changes Evolution is limited by the existing variations – adaptations are those that help an individual survive and reproduce Adaptations are often compromises Chance, natural selection, and the environment interact